1. Field of the Invention
The present invention relates to a radiation-sensitive resin composition, a polymer, and a resist pattern-forming method.
2. Discussion of the Background
Chemically amplified radiation-sensitive resin compositions generate an acid upon irradiation with an electron beam or far ultraviolet ray typified by a KrF excimer laser or ArF excimer laser at a light-exposed site, and a chemical reaction that proceeds with an aid of the acid as a catalyst allows the difference in dissolution rates in developing solutions to be produced between the light-exposed site and the light-unexposed site, thereby enabling resist patterns to be formed on the substrate.
Of these radiation-sensitive resin compositions, as lithography materials for an ArF excimer laser as a light source that enable microfabrication with light at shorter wavelengths, a resin composition containing as a constitutional component a polymer having in the skeleton an alicyclic hydrocarbon that does not exhibit significant absorption in the area of 193 nm and provide high etching resistance has been used. Furthermore, positive type radiation-sensitive resin compositions typically contain a polymer which generates a polar group through the elimination of a protecting group by the action of an acid to render the polymer itself alkali-soluble, and specific alicyclic hydrocarbon groups have been proposed as the protecting group (see Japanese Unexamined Patent Application, Publication No. H9-73173). Moreover, a technique has been investigated for reducing LWR (line width roughness) of a line-and-space pattern by employing a protecting group of a specific structure (see Japanese Unexamined Patent Application, Publication Nos. 2008-308545 and 2008-308546). Furthermore, a technique is also known for improving resolution as well as coarseness and fineness dependence by combining specific protecting groups (see Japanese Unexamined Patent Application, Publication Nos. 2002-372784 and 2003-84438).
However, at present, microfabrication of resist patterns has reached the level of a line width of no greater than 90 nm, and not only the improvement of basic properties such as the improvement of the resolving ability and the lowering of the LWR as mentioned above, but also other additional performance have come to be required. For example, in a resist pattern, as a line width of the resist pattern becomes narrower, the aspect ratio of the resist pattern becomes larger, and the resist pattern, in turn, is more prone to collapse. Therefore, it is more strongly required that a limit dimension for pattern collapse, which is a limit value for causing the resist pattern not to collapse, is low. On the other hand, in the formation of the resist pattern, reduction of a film thickness of the resist coating film typically occurs after development. If an amount of residual resist film is low at this stage, a disadvantage likely to be raised that the resist pattern are incapable of sufficiently serving as a mask in an etching step, leading to unsatisfactory etching. In particular, these days when further thinning of resist coating films is advancing, the influence of the reduction of the amount of residual resist film becomes increasingly more significant. Thus, there is a need for a radiation-sensitive resin composition exhibiting excellent LWR feature, as well as a low limit dimension for pattern collapse, and a large amount of residual resist film.